CHo.CO. Benzaldehyde and acetone combine under these
conditions to form benzylidene- and dibenzylidene-acetone3
C6H5COH + CH3.CO.CH3= C6H5CH:CH.CO.CH3.
2C0H5COH + CH3.CO.CH3 = C6HBCH:CH.CO.CH:CH.C6H3.
All the unsaturated acids have the following properties in-
common. They form additive compounds with nascent
hydrogen, halogen acids, and the halogens. On oxidation with
alkaline permanganate in the cold, they take up two hydroxyl
groups to form a dihydroxy-derivative, and, on further oxidation,
ultimately divide at the double link. Cinnamic acid may be
taken by way of illustration. On reduction it forms phenyl-
propionic acid, with hydrobromic acid, /3-bromophenylpropionic
acid (the bromine attaching itself to the /3-carbon, see p. 253),
with bromine a/3-dibromophenylpropionic acid, on oxidation with
permanganate, phenylglyceric acid and then benzaldehyde and
QI15CH:CH.CO.OH + H2 = C6H5CHo.CH2.CO.OH.
CBH5CH:CH.CO.OH + HBr = CfiH6CHBr. CHo.CO. OH.
Phenyl /3-bromopropionic acid.
C6HBCH:CH.CO.OH + Br2 = C6H5CHBr.CHBr.CO.OH.
Phenyl a/3-dibromopropionic acid.
C(iH5CH:CH.CO.OH + H2O + O = CeH5CHOH.CHOH.CO.OH.
CCHSCII:CH.CO.OH + 2O.2 = C6H5COH + 2CO2 + H2O.
The chief difference between the two groups of a/3 and /3y
unsaturated acids lies in the behaviour of the additive compounds
which they form with hydrobromic acid and bromine.
In the case of the a/3 acids, the hydrobromide of the acid, on
boiling with water, yields the corresponding (B hydroxy-acid,
and, on boiling with alkalis, a mixture of the original acid and
the unsaturated hydrocarbon, formed by the elimination of
carbon dioxide and hydrobromic acid,
1. C,H,CHBr.CIL,COOH + H2O = C0HBCHOH.CH3.COOH4-HBr.
* l ~ /3-Oxyphenyl-propionic acid.
2. C,IIrCHBr.CH.,.COOH + NaOH = CBH8CH:CH.COOH + NaBr
0 - Cinnamic acid. + H2O.
^ C,.II,CHBr.CII.,.COOII +NaOH = C6HaCH:CI-Ia + CO2 +KaBr
°' ^b ° - Styreiie. 4-IJ,O.
COHEN'S ADV. P. O. C. x